• Question: What are gravity waves?

    Asked by Hannah to Greg, Laura, Mobeen, Paul on 16 Mar 2016.
    • Photo: Paul O'Mahoney

      Paul O'Mahoney answered on 16 Mar 2016:

      Gravitational waves are thought to be ripples that are sent through space-time (the fabric of our universe, as many sci-fi shows say) because of the interaction of objects. So sort of like dropping a stone in to a lake, the ripples of water are like the ripples in space-time, with the gravitational waves moving out the speed of light.

      I think it is the LIGO group who recently detected gravitational waves, there is a really good article here which goes in to a bit more detail of what they found and how they found it: https://www.theguardian.com/science/2016/feb/11/gravitational-waves-discovery-hailed-as-breakthrough-of-the-century

    • Photo: Greg Melia

      Greg Melia answered on 16 Mar 2016:

      There are four forces in the universe: the weak nuclear force, the strong nuclear force, electromagnetism and gravity. Gravity, despite being the one we feel and use everyday, is by far the weirdest force, and the one that we understand the least. We can understand the other three forces by thinking about particles and waves interacting – and understanding how they interact at an atomic or subatomic level is what quantum physics is all about. The problem with gravity is that it attracts objects over much longer distances than the other three forces, particle-based explanations of gravity are deeply unsatisfactory, because to work over long distance, those particles would have to travel faster than the speed of light, which isn’t allowed by Einstein’s equations.

      Einstein solved this problem by saying that gravity curves spacetime and objects follow the curvature of spacetime: if you imagine that spacetime is a sheet and you put a football in the middle of that sheet so it curves down and other objects on the sheet roll towards it, you’ve got the picture. What that meant was that if two huge objects collided, we should be able to detect little ripples in spacetime – gravitational waves – coming from the collision site. Recently we were able to do exactly this when two black holes collided. It showed that Einstein’s predictions, made over 100 years before, had been bang on, and his theories were sound.

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